Operating means for four-way view finder mats



Oct. 27, 1936. G. A. MITCHELL 2,058,313

OPERATING MEANS FOR FOUR-WAY VIEW FINDER MATS Filed o t. 16, 1955 3 Sheets-Shee 1 I I I I /a "I @f 4 J/ Z6 59 3 menforj. GEO/:96, ,9. Mz'fc/z ell Oct. 27, 1936. GPA. MITCHELL 8,

OPERATING MEANS FOR FOUR-WAY VIEW FINDER MATS Filed Oct. 16, 1953 3 Sheets-Sheet 2 1 210622 ha)". Gearye. fl/Vz'fc/ze/Z l atented Oct. 27, 1936 PATENT OFFICE OPERATING MEANS FOR, FOUR-WAY- VIEW FINDER MATS George A. Mitchell, Beverly Hills, Calm, assignor to Mitchell Camera Corporation, West Hollywood, Calif., a corporation of Delaware Application October 16, 1933, Serial No. 693,739

' Claims. (01. 88-15) This invention relates generally to focusing or view finding instruments having adjustable matting devices as used in motion picture cameras. The present invention is particularly adapted to and designed for use in the usual view finder used in connection with motion picture cameras, and -may be considered in one aspect as an improvement on a motion picture view finder matting device disclosed in Patent -No. 1,921,191, issued to Jonson and Grebe on August 8, 1938, Ser.- No. 543,120. In its broader aspects, however, the

present invention is not limited to any particular,

,type of matting arrangement.

Motion picture cameras are ordinarily adapted to use with a number of photographic objectives of various focal lengths, and since the field of View taken in by a lens depends uponits focal length, the field of view spread upon the film (or ground glass of the focusing instrument) varies with the focal length of the camera objective in use. Since it is desirable that the field of view framed within the view finder instrument corresponds to the field of view spread on the film by the photographic lens, it accordingly becomes necessary to change the field of view within the view finder with each lens change in the camera.

The Jonson and Grebe patent referred to above disclosed a novel four-way adjustable mat arrangement within the view finder, adapted to be operated to vary the field of view framed within the view finder to bring it into correspondence with that spread on the film by the particular lens then in the camera. The view finder to which said invention particularly appertained comprised an elongated casing forming a light conduit, and having an objective at its forward end and a ground glassto therear thereof on which the image was formed, the casing being of a cross sectional size but slightly larger than the largest image area to be framed and viewed on the ground glass. Jonson and Grebe provided fourway mats which moved in suitable guides trans- .versely across the instrument in front of the ground glass to form an adjustable rectangular aperture, and the mats were formed of flexible material and were flexed and turned rearwardly at right angles and guided along .the inner surface of the walls of the instrument casing. Attached to the rear turned end of each mat was a slide plate by which the mat was moved along the casing wall and through its right angle bend to move transversely across the casing. The

slide plates were each formed with rack teeth meshing with a gear mounted on the instrument and operated by an adjustment knob. There was thus one knob for each of the four mats, and four individual adjustments were accordingly required to frame the view in the finder.

It is a primary object of the present invention to provide a view finding instrument having a four-way matting arrangement of the general type described, with means interconnecting opposing mats to operate toward and from each other in unison whereby each pair of opposing mats may'be controlled by a single operating means.

Certain substantial difficulties are encountered in inter-connecting opposing mats to operate in unison with the type of instrument referred to, due to the fact that the view finding casing is just slightly larger in cross sectional area than the largest image to be framed on the ground glass, and the interconnecting means must be so arranged as not to interfere with the image on the ground glass. The manner by which I have overcome these difiiculties is a feature of the invention, but this will be left to be explained in more detail in the body of the specification.

It is a further object of the invention to. provide the mat operating members with suitable calibrated scales, whereby the mats may be set merely by reference to these scales, in contradistinction to past practice wherein individual mats were lined up by reference to the view area as observed through the focusing instrument of the camera.

The invention itself, as well as additional objects and features, will now be best understood by referring to the following detailed description of a present preferred embodiment thereof, reference for this purpose being had to the drawings, in which:

Fig. 1 is a side elevation of a conventional motion picture camera provided with a view finder;

Fig. 2 is a plan view looking down on the view finder shown on the camera of Fig. 1;

Fig. 3 is a horizontal longitudinal section taken through the view finder as indicated by line 3-3- of Fig. 1, the objective combination not being shown in section;

Fig. 4 is a section taken as indicated by broken line 4-4 of Fig. 3;

Fig. 5 is a transverse section taken as'indieated by line s-5 of Fig.3;

Fig. 6 is a transverse section taken as indicated by broken line 6-6 of Fig. 3;

Fig. 7 is a side elevation detail of the mat framing device;

Fig. 8 is a a detail looking down on'the device shown in Fig. 7;

Fig. 9 is a detail taken on line 9-9 of Fig. 4; and

Fig. 10 is a section taken on line il0 of Fig.

In the drawings there is shown at ID a cone ventional motion picture camera comprising base If, head l2 rising from the front end of said base and carrying lens mount l3 supporting photographic objective 14, camera box i5 supported on base II to the rear of head l2 and transversely slidable in ways l6, and film magazine I8 mounted on box I5. Within box I5 is the usual exposure aperture plate and intermittent mechanism for moving the film past the plate, these parts not being illustrated since they may be of any conventional design. Before photographing a scene, an objective lens I4 of proper focal length is placed in mounting 13. Box i5 is then moved transversely in ways ii to bring a focusing device 29, carried by the side wall of the box, into alinement with the objective. The objective may then be accurately focused on the screen by looking into the focusing device and moving the objective forwardly and rearwardly until the image appears sharp on the ground glass. At this time the mats of the view finder may be adjusted to correspond with the field of view of the camera lens, and the finder may be alined with the scene.

The finder, indicated generally at 25, is carried at the side of the camera .outside of focusing device 20, as on a bracket 29, and this bracket may have provision for swinging the finder in a hori- .zontal plane, as on a pivot' 24, to aline the finder with the scene, or in other words to adjust for parallax. A present preferred view finder mount ing, indicated in thedrawlngs, is disclosed and claimed in my application entitled Swinging finder mounting, Ser. No. 693,738, filed Oct. 16, 1933, which has matured into U. S. Patent 2,012,- 514, issued August 2'1, 1935. After the camera objective is focused and the finder is adjusted, the camera box is returned to its initial position to bring the aperture plate and film back into alinement with the objective. when this is accomplished, the same field of view then spread on the film is framed within the view finder.

The view finder proper comprises a casing forming a light conduit and made up of vertical side walls 29 and 2'land top and bottom walls 28 and 29, respectively, the casing being rectangular in cross-section (see Fig. 5). The forward end of the finder body is comprised of a mounting casting 90, which has the pivot mounting 24 heretofore referred to, and carries the finder objective combination 9|. This objective combination is preferably an erecting combination giving an image which is right side up and correct as for right and left, such a combination being described in my patent No. He. 17,995, entitled "Erecting finder." Means for automatically focusing said combination, if desired, may be such as disclosed in the application referred to above Ser. :No.. 693,738, which has matured into U. 8. Patent 2,012,514, issued August 27, 1935. The upper and lower walls of casting Ill and the finder body are parallel, while the side walls thereof diverge rearwardly from the objective combination to a point 92 somewhat to the rear of the center of the finder body, and then extend parallel to each other to the rear end of the finder (see Fig. 3). The walls 24, 21, 28, and 29 of the finder casing fit over a reduced extension 34 of mounting casting "so as to be flush with the outer surface thereof, and are fastened to said casting as by screws 35. The top and bottom finder cas- Fig. 3.

ing walls 29 and 29 are formed along their longitudinal edges with flanges 38 adapted to fit over side walls 26 and, and screws 31 fasten said flanges to walls 26 and 21.

Mounted to the rear of the objective combination in the divergent section of the corresponding casing, and located properly with respect to the focal plane of the-objective combination, is a glass 40 having a suitable image receiving surface 4| on its forward side, surface 4| being at the focal plane of the objective. This image receiving surface 4i may, for instance, be a ground glass surface. Glass 40, which is rectangular in configuration, is preferably a pianoconvex lens, its forward plane surface being ground as mentioned, and its rearward surface being slightly convex so that the lens acts as a light collector. It may here be stated that, in the present form of the invention, the framing of the field of view in the view finder is accomplished directly in front of ground glass surface 4|, as will be more fully described hereinafter. To the rear of lens 40 may be another collecting lens 43, as shown in Fig.3.

Lens 40 is mounted in a frame comprising upright members 46 having grooves 4'! within which the vertical edges of the lens are received (Fig. 3)., a horizontal lower member 48 supporting the lower edge of the lens and secured, as by welding, between the lower ends of members 45, F

and a horizontally extending upper member 49 which may be frictionally held between the upper ends of members 46. Upright members 46, which are slightly spaced from the side walls of the casing to provide for passage of the later described mats (Figs. 3 and 6), are secured top and bottom at their forwardly facing surfaces 59 to upper and lower horizontal members 5| and 52, respectively, the ends of said members 5| and 52 engaging the side walls 26 and 21- of the easing and beingsecured thereto as by screws 54. The upper and lower surfacesof members 5| and 52, respectively, engage the inner surfaces of the casing walls, while the upper and lower hori' zontal lens frame members 49 and 48, respectively,

metal, or any other suitable flexible material, a

curve fromthe ends of grooves 55 around the outer edges of uprights 46 and extend rearwardly outside said uprights along the inner surfaces of casing sidewalls 25 and.21, as clearly shown in The mats are individually operable to slide in grooves or ways 50 for the purpose of adjusting the side or vertical edges of the field of view in front of the ground lass by forward or rearward movement of rearwardly extending slide members or plates 58 amxed thereto, as by rivets 59.

The inwardly facing surfaces of upright frame members 48 are formed just forwardly of lens 40, with grooves" providing a vertical way for fiexible upper and lower mats 6i and 52, respectively,

it being noted that said grooves 60 are in a plane back of the side mats, so that the upper and lower the same nature as the side mats, curve from the ends of grooves 88 around the outer edges of horizontal upper and lower frame members 88 and 48, respectively, and extend rearwardly along the inner surfaces of the respective upper and lower walls of the casing, their rearward ends being affixed, as by rivets G3, to rearwardly extending slide members or plates 84, which are movable forwardly or rearwardly to cause the mats to slide vertically in grooves 88 for the purpose of framing the horizontal edges of the field of view before the ground glass.

It will now be understood that forward or rearward movement of the rearwardly extending slide members attached to the flexible mat causes the mats to flex and slide around the edges of the lens frame and through the transverse ways in front of the ground glass whereby their straight horizontal and vertical aperture defining edges adjust the field of view at the ground glass. The mats, although flexible, possess sufficient thickness to stand in the position described and to be pushed forward by force applied at their rear edges. The mats preferably are cut out back of the view defining edge, as indicated at 66, leaving simply a narrow mat element or frame to define the view area so that it is possible to observe objects just outside the field of view, or to observe moving action just before it enters the field of view. The advantage of this provision is obvious to the camera operator. It is to be understood that when the claims refer to a mat, such anarrow frame, or mat element, is contemplated as within the meaning of that expression.

, Means now to be described are provided for interconnecting opposing matsto move in unison, and for operating each such pair of interconnected mats by a single operating means. There is utilized for each mat moving slide plate a gear meshing with rack teeth on said plate and operable in unison with the corresponding gear of the opposing mat. Thus the slide plates, which slide in ways 88 provided by guide strips 88 (see Figs. 3, 4, 5, and 6), are each provided with a longitudinally extending slot 18 having along one of its longitudinal edges rack teeth 1i, as clearly shown in Figs. 3 and 4.

Considering first the side mat 56 that moves adjacent the casing side wall 21, which sidewall is next to the camera, there is seen to be a gear 13 meshing with the rack teeth of the slider plate connected to said mat, and said gear is rotatable on a bearing bushing 14 mounted on the inner surface of casing side wall 21 by means of a screw 15 passing through said wall and screw threaded into the bushing, which bushing has a reduced end 14a set into the casing wall. Bushing 14 has a flange 16 confining gear 18 thereon. Gear 18 meshes with a larger gear 18 directly above it which is rotatable in a similar manner on a bearing bushing 18 mounted on casing side wall 21. Gear 18 is formed at 18a to clear guide strip 88 and slide plate 58.

Above and slightly rearward of gear 18 is a smaller gear 88 meshing therewith, said gear '88 just clearing upper casing wall 28 as shown in Fig. 4. Gear 88 is mounted on a horizontal shaft 8i extending across the view finder casing adjacent upper casing wall 28 and mountedjat its ends in suitable bearings 82 carried by the casing side within the device and upper casing wall 28, and

accordingly does not interfere with the view area of the light conduit.

n the. opposite end of shaft 8|, adjacent the inner surface of casing side wall 26, is a gear 84 similar to gear 88, and gear 84 meshes with a gear 85 mounted on wall 25 directly across from and.

similarly mounted to the aforementioned gear 18 on opposite side wall 21. Gear 85 meshes with a gear 86, similar to and directly across from the aforementioned gear .13, gear 88 being mounted fast on the inner reduced and 81 of the center shaft 88 of side mat operating knob 88.

Gear 86 meshes with the rack teeth 1| of the mat operating slide plate 58 that moves adjacent side wall 26, and it will be evident that the gear train described interconnects the two side mat operating slide plates and thus constrains the opposing side mats to move in unison toward and from each other.

A mounting disc 88 for knob 88 is mounted adjacent the outer surface of side wall 28 and is fastened thereto by screw 8|, said screw 8| serving also as a mounting for the bearing bushing on which gear 85 is mounted. Mounting disc 88 has an axial bore 82 and an outwardly extending annular flange 83 defining said bore. A bushing 94 having an external flange 85 adapted to engage the end of flange 83 is force fitted within bore 92 and extends through casing wall 26, as shown, the engagement of bushing flange 85 with flange .83 accurately positioning the bushing. The center shaft 88 of knob 88 has a free turning fit within the bore of bushing 84, and knob 88 has an annular bearing surface 81 which engages and rotates on the outer end of bushing 88. Gear 88 is fastened on the reduced inner end- 81 of center shaft 88 by fiat headed screw 88, and gear 86 engages the inner end of bushing 84 to confine the knob in axial position.

Knob 88 has an outer knurled or milled rim portion 88 for convenience in gripping, and adjacent said milled portion has a flange I88 of slightly reduced diameter which comes against and rotates on the outer surface of mounting disc 88, the outer periphery of said flange l88'being of the same diameter as disc 88. Disc '88 is formed with an indicating mark I82 (see Fig. 5) and the outer peripheral surface of knob portion I88 is inscribed with a suitably calibrated scale, reading for instance in focal lengths of camera objectives.

It will be understood that manual rotation of knob 88 acts through the described gearing to move the two side mats back and forth in unison, and that knob 88 accordingly constitutes a single operating means for the two opposed side mats. To adjust the two vertical edges of the fleld of view framed within the view finder to correspond with that spread on the film by a camera objective of given focal length, it is only necessary to rotate the side mat controlling knob to the proper position for that focal length lens, as indicated by the scale inscribed on the" knob.

The proper initial setting of the two side mats- 28 has been put in place. Likewise, the proper.

setting of the calibrated knob 88 relative to the two mats can be adjusted by rotating the knob relative to gear 88 before screw 88 is set up.

The rack teeth 1| of the slider plate 84 connected to the lower mat are engaged by a gear H8, which is rotatable on a bearing bushing Ill similar to previously described bushing 18) mounted on lower casing wall 29. This gear H8 meshes with a larger gear H4 mounted to one inner surface thereof.

side thereof on a bearing bushing II3 similarly mounted on wall 23, gear II4 being formed at II3 to clear guide strip 33 and slider plate 34. Gear I I4 meshes with a smaller gear I I3 mounted close to sidewall 21, gear I I3 being on the lower end of a vertical shaft I20 journaled at its upper and lower ends in suitable bearings I2I and I22 mounted on upper and lower casing walls 23 and 23, respectively. This sh'aft I20 is disposed between the outer limit of the largest view area to be framed within the instrument and the adjacent casing side wall 21, so that the .view area of the light conduit is not interfered with by the presence of the shaft. On the upper end of the shaft, just below upper casing wall 20, is a gear I24 similar to gear I I3 and gear I24 meshes with a larger gear I25 directly opposite and similar to the aforementioned gear II4, said gear I25 being mounted on a bearing bushing I23 fastened in place in upper casing wall 23 by flat headed screw I21.

Gear I25 meshes with a gear I30 fastened, as by rivct ill, on the lower end of an operating knob center shaft I32 that extends downwardly through an opening in casing top wall 23. Surrounding shaft I32 is a gear sleeve I33 having on its lower end, adjacent gear I30, a gear I34 of the same diameter as gear I30. Said gear I34 meshes with therack teeth H on the upper mat slider plate 34. Gear I30 on shaft I32 is capable of being rotatably adjusted with reference to gear I34 on sleeve I33, but during operation gears I30 and I34 are locked securely together, as later to be described.

Gear sleeve I33 is mounted to rotate in the axial bore I33 of a mounting disc I33 mounted on the upper surface of easing wall 23 and fastened thereto as by rivet I40. The lower side of disc I33 has a coaxial boss I which extends through casing wall 23 and is flush with the A ring I44 of the thickness of disc I33 is relativelyrotatable on the periphery of said disc, and means are provided for fastening ring I44 to the disc after proper rotatable adjustment thereon. For instance, ring I44 may be provided with circumferential slots I45 through which pass clamping screws I46 which screw thread into the periphery of disc I33, their heads engaging ring I44 (see Fig. 5). hereinafter.

A circular plate I43 or the diameter of ring I44 is mounted for rotation on the upper side of said ring. This plate I43 has a central upwardly extending boss I43 and an axial bore I50 through which extends the upper end of gear sleeve I33, said plate and gear sleeve being fastened rigidly together as by means of pin I5I. The lower side of plate I43 has a counter bore I52 within which is taken an upwardly extending boss I53 of the aforementioned disc I33, plate I43 having bearing on the upper end of said boss. The under side of plate I43 also has a larger counter bore I55 to accommodate certain parts to be described later. Thus gear sleeve I33 and plate I43 are rigid with one another and are supported on disc I33 and ring I44.

Knob center shaft I32 has near its upper end an annularflange I30 which rests on the upper end of gear sleeve I33 and boss I43. Mounted on the upper end of shaft I32 is an operating knob I32, which is counterbored at I33 to receive boss I43 and center shaft flange I30, and has bore I34 through which extends the upper The purpose of this adjustment will appear extremity of shaft I32. The knob is fastened to shaft flange I30 as by rivet I35.

The underside of knob I32 comes against the upper side of plate I40, but these parts are rotatably adjustable with reference to each other. An adjustment screw I33 whose head is countersunk in the uppersurface of knob I 32 extends downwardly and screwthreads into a flanged bushing I31 mounted in an arcuate slot I63 in circular plate I43 (see Fig. 10), the lower end -of said bushing having flange I33 of a diameter greater than the width of slot I33 and which engages the underside of plate I43 at the edges of said slot. It will be evident that when screw I33 has been loosened knob I32 may be rotated relatively to plate I43, within the limits set by the length of slot I33, and by tightening screw I33 knob I32 is securely locked to plate I43. It is this adjustment that enables proper setting of the angular relation between gear I30 which is rigid with the knob and the gear I34 that engages the rack teeth of the upper mat slider plate. With the several adjustments all proper- Iy made, and with screw I33 tightened, rotation of knob I32 then rotates gears I34 and I30 in unison, and so operates the upper mat directly through the slider plate engaged by gear I34 and the lower mat through gear I30 and the described gear train between gear I30 and the slider plate connected to the lower mat.

The construction described -enables relative adjustment of the upper and lower mats for the purpose of centralizing the opening therebetween, either for the purpose of initial adjust ment, or in the event the finder should become sprung out of position in a vertical position. To make such an adjustment, the screw I33 that fastens knob I32 to plate I43 (and thus locks gears I30 and I34 together) is loosened, and the knob I32 is then rotated relative to plate I43 until the inner view defining edges of the upper and lower mats are observed to be at equal distances from the horizontal cross-hair. When this adjustment is correct screw I33 is set up.

The calibrated scalefor upper and lower mats is inscribed in focal lengths of camera lenses on the outer periphery of circular plate I43 and an indicating mark I1I is inscribed on the adjustable ring I44, as clearly shown in Fig. 5. To coordinate the vertical distance between the inner view defining edges of the upper and. lower mats with this calibrated scale reading as indicated by mark "I, screws I43 are loosened and ring I44 rotated sumciently to make the adjustmerit.

With the several initial permanent adjustments properly made, the four view finder mats are adjusted. to the proper view area for any focal length lens to be used in the camera simply by turning the two mat operating knobs to the proper positions as indicated by their calibrated scales.

It will be understood the drawings and de scription are merely illustrative of and not restrictive on the broader claims appended hereto, for various changes in design, structure and arrangement may be made without departing from the spirit and scope of said claims.

I claim:

1. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image is formed in a focal plane transverse of the casing, four flexible mats, means for guiding said flexible mats in said focal plane and in planes along the walls of said casing, one along each wall, separate gear trains mounted on theeach of said gear trains.

2. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image is formed in a focal plane transverse of the casing, four flexible mats, means for guiding said flexible mats in said focal plane and in planes along the walls of said casing, one along each wall, separate gear trains mounted on the casing walls interconnecting the two mats moving along each pair of opposite casing walls to move in unison toward and from each other in said focal plane, said gear trains each including a shaft extending across the casing interior outside thelimits of the light conduit view area for transmitting gear train motion between mats moving along opposite casing walls, and a manual operating means for each of said gear trains.

3. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image, is formed in a focal plane transverse of the casing, four flexible mats, means for guiding said flexible mats in said focal plane and in planes along the walls of said casing, one along each wall, slide members in the last mentioned planes operatively' connected to the mat portions in said planes, rack gear teeth on each of said slide members, a pinion gear supported on each of the casing walls meshing with therack teeth on the corresponding slide member, separate sets of gear means operatively interconnecting the pinions on each pair of opposite casing walls, whereby the mats moving along opposite, casing walls move in unison toward and from each other across the focal plane, and manual means for independently'operating each of said sets of gear means and pair of mats connected thereto.

4. In an optical device having longitudinally extending casing walls defining a light conduit of rectangularcross section in which an image is formed in a focal plane transverse of the casing, four flexible mats, means for guiding said flexible mats in said focal plane and in planes along the walls of said casing, one along each wall, slide members in the last mentioned planes operatively connected to the mat portions in said planes, rack gear teeth on each of said slide members,-a pinion gear supported on each of the casing walls meshing with the rack teeth on the corresponding slide member, separate sets of gear means operatively interconnecting the pinions on each pair of opposite casing walls, whereby the mats moving along opposite casing walls move in unison toward and from each other across the focal plane,

, and an operating knob for each of the two intermembers in the last mentioned-planes operatively connected to the mat portions .in said planes, rack gear teeth on each of said slide members, a pinion gearsupported on each of the casing walls meshing with the rack teeth on the corresponding slide member, two shafts extending across the casing interior in directions at right angles to each other and journalled at their ends in the casing walls, said shafts disposed outside the limits of the view area of the casing, a pinion gear on each end of each of said shafts adjacent the inner surface of the corresponding casing wall and geared to the rack operating pinion gear on that wall, the gearing being so arranged that the mats moving along opposite side walls move in unison toward and from each other across the focal plane, and a single manual member for independently operating each pair of gear interconnected mats. I I

6. In an optical device having longitudinally extending casing walls defining a' light conduit of rectangular cross section in which an image is formed in a focal plane transverse of the casing, a pair of flexible mats, means for guiding said flexible mats in planes along opposite side walls of said casing and in said focal plane, the inner ends of said mats defining opposite edges of the view area at said focal plane, slide members in the first mentioned planes operably connected to the mat portions in said planes, rack gear teeth on each of said slide members, a pair of pinion gears, one meshing with the rack teeth on each of said slide members, bearing means supporting, one of said pinion gears on the casing wall, an operating knob having a center shaft extending inwardly through and supported by the opposite casing wall and having rigidly mounted on its inner end the other of said pinion gears, and a gear train interconnecting said pinions to cause said slide members and mats to operate in unison.

7. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image is formedin a focal plane transverse of the casing, a

pair of flexible mats, means for guiding said flexible mats in planes along opposite side walls of said casing and in said focal plane, the inner ends of said mats defining opposite edges of the view area at said focal plane, slide members in the first mentioned planes operably connected to the mat portions in said planes, rack gear teeth on each of said slide members, a pair of pinion gears, one meshing with the rack teeth on each-of said slide members, bearing means supporting one of said pinion gears on the adjacent casing wall, an opwardly through the opposite casing wall and extending through the other of said pinion gears, said shaftbeing relatively rotatable within its surrounding pinion gear, a sleeve rotatably mounted on said knob center shaft and made rigid with said last mentioned pinion gear, means for locking said sleeve in adjusted rotative position relative to said shaft, a pinion gear rigidly mounted on the inner end of said knob center shaft, and a gear train interconnecting the pinion gear on erating knob having a center shaft extending insaid knob center shaft and the pinion gear on the opposite casing wall to cause said slide members and mats to operate in unison.

8'. In an optical device having longitudinally extending casing walls defining a light conduit of.

rectangular cross section in which an image is formed in a focal plane transverse of the casing, a

pair of flexible mats, means for guiding said flexieach of said slide members, a pair of pinion gears,

one meshing with the rack teeth on each of said slide members, bearing means supporting one of id pinion gears on the adjacent casing wall, an operating knob having a center shaft extending inwardly through the opposite casing wallconcentric with the other of said pinion gears, a sleeve relatively rotatable on said center shaft, means on the knob for locking said sleeve in ad justed rotative position relative to said shaft, another pinion gear concentric with the last mentioned pinion gear, the last two mentioned pinion gears being fast one on the knob center shaft and the other on the surrounding sleeve, and a gear train interconnecting that one of the two last mentioned concentric pinion gears that does not mesh with the rack teetl. of the slider plate, with the inion gear on the opposite casing wall to cause said slide members and mats to operate in UlllSOll. I

9. In an optical device having a casing defining a light conduit, a p, ir of mats oppositely movable across the light conduit, a mat operating knob having a center shaft mounted for rotation on the casing, a sleeve relatively rotatable on said cen ter shaft, a plate rigidly mounted on said sleeve adjacent said knob, means for locking said plate to said knob in adjusted rotative positions relative to one another, a pair of concentric pinion gears mounted one on the sleeve and one on the center shaft, and gear means interconnecting said gears respectively with the two mats to move said mats in opposite directions as the knob is rotated.

10. In an optical device having a casing defining a light conduit, a pair of mats oppositely movable across the light conduit, a mat op;- erating knob having a center shaft mounted for rotation on the casing, a sleeve relatively rotatable on said center shaft, a clamping plate rigidly mounted on said sleeve adjacent said knob, an arcuate slot in said plate, a clamping screw extending through said knob and areuate slot, a. nut member on the lower end of said screw adapted to bear on said clamping plate, a pair of concentric pinion gears mounted one on the sleeve and one on the center shaft, and gear means interconnecting said gears respectively with the two mats to move said mats in opposite directions as the knob is rotated.

11. In an optical device having acasing de fining a light conduit, a pair of mats oppositely movable across the light conduit, a mat operating knob having a center shaft mounted for rotation on the casing, a sleeve relatively rotatable on said center shaft, a circular plate rigidly mounted on said sleeve adjacent said knob, means for locking said plate to said knob in adjusted rotative positions relative to each other, a calibrated scalc inscribed on the periphery of said' circular plate, a member adapted to be mounted independently of the knob adjacent said circular plate. and bearing an indicating mark adjacent said scale, said member being circularly adjustable with reference to said circular plate, a pair of concentric pinion gears mounted one on the sleeve and one on the center shaft, and gear means interconnecting said gears re-- spectively with the two mats to move said mats in opposite directions as the knob is rotated.

12. In an optical device having a casing defining a light conduit, a pair of mats oppositely movable across the light conduit, a mat operating knob having a center shaft mounted for rotation on the casing, a sleeve relatively rotatable on said center shaft, a circular plate rigidly mounted on said sleeve adjacent said knob, means for locking said plate to said knob in adjusted rotative positions relative to each other, a calibrated scale inscribed on the periphery of said circular plate, a circular mounting disk of diameter less than said plate having an axial bore providing bearing for said sleeve, said disk adapted to be mounted on said casing, a ring rotatable on the periphery of said disk adjacent said circular plate and bearing an indicating mark adjacent said scale, means for setting said ring relative to said disk, a pair of concentric pinion gears mounted one on the sleeve and one on the center shaft, and gear means interconnecting said gears respectively with the two mats to move said mats in opposite directions as the knob is rotated.

13. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image is formed in a focal plane transverse of the casing, a pair of mats oppositely movable across said light conduit at said focal plane, a pair of racks for operating said mats to move in opposite directions, a pair of pinion gears, one meshing with each of said racks, bearing means supporting one of said pinion gears on the adjacent casing wall, an operating knob having a center shaft extending inwardly through the opposite casing wall and extending through the other of said pinion gears, said shaft being relatively rotatable within its surrounding pinion gear, a sleeve rotatably mounted on said knob center shaft and made rigid with said last mentioned pinion gear, means for locking said sleeve in adjusted rotative position relative to said shaft, a pinion gear rigidly mounted on the inner end of said knob center shaft, and a gear train interconnecting the pinion gear on said knob center shaft and the pinion gear on the opposite casing wall in such manner that the mats will move to and from each other.

14. In an optical device having longitudinally extending casing walls defining a light conduit of rectangular cross section in which an image is formed in a focal plane transverse of the easing, a pair of mats oppositely movable across said light conduit at said focal plane, a pair of racks for operating said mats to move in opposite directions, a pair of pinion gears, one meshing with each of said racks, bearing means supporting'one of said pinion gears on the adjacent casing wall, an operating knob having a center shaft extending inwardly through the opposite casing wall concentric with the other of said pinion gears, a sleeve relatively rotatable on said center-shaft, means on the knob for locking said sleeve in adjusted rotative position relative to said shaft, another pinion gear concentric with the last mentioned pinion gear, the last two mentioned pinion gears being fast one on the knob center shaft and the other on the surrounding sleeve, and a gear train interconnecting that one of the two last mentioned concentric pinion gears that does not mesh with the rack, with the pinion gear on the opposite casing wall, in such manner that the mats will move to and from each other. 4

15. In an optical device having longitudinally extending casing walls defining a light conduit in which an image is formed in a. focal plane transverse of the casing, a pairof mats oppositely movable across said light conduit at said focal plane, anoperating knob outside one casing wall having a center shaft extending inwardly through said casing wall and a sleeve rotatably mounted on said center shaft and also extending through said casing wall, means for locking said sleeve 10 in adjusted rotative position relative to the center shafha pair of concentric pinion gears disposed adiaoent to one another inside said casing wall and mounted one on the knob center shaft and one on the surrounding sleeve, and a pair of racks, one operated by each of said pinion gears, said racks being connected each to one of the mats and moved by unitary operation of the respective pinion gears as the knob is turned to move the mats in opposite directions.

GEORGE A. MITCHELL. 

